Stub axle

Abstract

A stub shaft for a turbine engine is described in which respective masses are positioned along the stub shaft in a balanced rotation relationship for normal rotation. One mass is positioned at the periphery of a shaft end rim such that upon failure of the stub shaft this mass is detached. Such displacement or detachment of the mass causes imbalance which creates vibration which in turn causes surge within a compressor associated with the stub shaft as well as possibly interference engagement with stable structure elements in order to limit turbine and/or compressor over speed.

1. A stub shaft for a turbine engine, the shaft comprising a shaft end associated with a compressor, the shaft characterised in that a failure mass is secured upon the shaft end and an intermediate mass secured at an intermediate location on the shaft and a balance mass providing rotational balance for the shaft in normal use whereby upon failure of the shaft the failure mass is displaced and the shaft vibrates to cause compressor surge. 
   
   
     2. A stub shaft as claimed in  claim 1  wherein the shaft end is forward of a mounting for the stub shaft. 
   
   
     3. A stub shaft as claimed in  claim 1  wherein the vibration causes radial displacement of the stub shaft whereby there is interference engagement with stable structures to drag brake the shaft and limit rotational speed of the turbine or compressor. 
   
   
     4. A stub shaft as claimed in  claim 1  wherein the shaft end is bell shaped. 
   
   
     5. A stub shaft as claimed in  claim 4  wherein the failure mass is secured at a rim of the bell shape. 
   
   
     6. A stub shaft as claimed in  claim 4  wherein the intermediate mass is secured at a crown part of the bell shape. 
   
   
     7. A stub shaft as claimed in  claim 1  wherein the balance mass is placed along a stub axle of the shaft to balance couple between the failure mass and the intermediate mass for rotational balance of the stub shaft in normal use. 
   
   
     8. A stub shaft as claimed in  claim 1  wherein one or more of the masses is moveable to achieve tuning of rotational balance for the stub shaft. 
   
   
     9. A stub shaft as claimed in  claim 1  wherein the balance mass is moveable when the failure mass is displaced upon failure of the shaft in order that the balance mass engages by interference a brake or stable structure to facilitate limitation of the rotational speed of the stub shaft. 
   
   
     10. A turbine engine incorporating a stub shaft as claimed in  claim 1 .